Why is restriced internal rotation first to be noticed in Hip Osteoarthritis?

[mhco]

Hi,

I have read that in Hip OA, restriction of internal rotation is the first movement which is noted to be lacking.

Does any know/have a logical guess as to why this is? Why not another movement eg flexion, or abduction?

Thanks

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[skiz knot]

It's been a while since I had to think about this but here it goes... If you subscribe to the belief that a good portion of OA in the hip is related to femoral-acetabular impingment then the CAM and/or Pincer Lesion is limited in FADIR position. Flexion, Adduction, and Internal Rotation.

 

[tymont12]

When internally rotating, you are exposing more of the femoral head to the acetabulum and therefore causing more contact between the arthritic surfaces. External rotation does the opposite. Thats why classic Netter drawings of hip OA show a person using a cane on an externally rotated hip.